With only 10 to go until SOHO's one thousandth comet has been
discovered (see related links below), there are still surprises to be
encountered: The so-called "Marsden group" of comets appears to
contain a close-knit family tree!

Nine comets observed by SOHO (C/1999 P6, P8, P9, N5 and J6, C/2005 E4,
G2, V9 and V10) are believed to make up two successive generations of
this family tree, shown above with a supposed (not observed)
"grandparent" that might have travelled near the Sun in 1993. The "X"
indicates that no return of C/1999 P6, P8 or P9 (nor children) was
observed. Presumably, they did not "survive" the 1999 encounter with
the Sun (all of their ice evaporated) or they were simply below the
brighness level detectable with LASCO in April/May of 2005.

Comet groups, and "families" like the one shown above, are the result
of fragmentation of the "parent bodies" near perihelion (the closest
approach to the Sun).

But the small family above is not the end of the story - there are
many other likely links between the almost one thousand comets
observed by SOHO: Comet 96P/Machholz 1 - observed by SOHO in 1996 and
2002 (a much more photogenic comet, as shown in the montage above) may
be the ancestor not only of the Marsden group of comets but also of
the Kracht I group. The relationship between the Marsden and Kracht I
groups is fairly obvious from the striking similarity of their orbits
- the link to 96P/Machholz 1 is harder to show, and may go about 4000
years back in time.

There's more - the Marsden and Kracht I groups, together with
96P/Machholz 1 may also be related to several meteor showers: The
closest link is between Marsden, Kracht I and the Daytime
Arietids. More distant links may exist also to the Quadrantids and the
Delta Aquarids meteor showers.

At the risk of overselling a point - that's still not all. The Kreutz
group of sungrazer comets also have a noble (though different)
lineage, if you believe the claims quoted in a nice article on this
subject by Tony Hoffman and Brian G. Marsden in the August 2005
edition of Sky
& Telescope. The two subgroups of Kreutz comets (I and II)
themselves contain the Great Comet of 1843 (Kreutz I) and the Great
Comet of 1882 as well as Ikeya-Seki (Kreutz II). The latter two may be
the result of a splitting of the AD 1106 comet. And perhaps (though
not supported by much evidence), they're all related to a comet
reported to be seen splitting in 372 BC by Greek philosopher Ephorus!

Now that is something to ponder about while waiting for SOHO-1000 to
be announced!